US3888625A

US3888625A - Method of chrome-retanning leather

Info

Publication number: US3888625A
Application number: US327574A
Authority: US
Inventors: William Orval Dawson
Original assignee: Chemtan Co
Current assignee: Chemtan Co
Priority date: 1973-01-29
Filing date: 1973-01-29
Publication date: 1975-06-10
Anticipated expiration: 1992-06-10
Also published as: GB1416641A

Abstract

An improved process of chrome-retanning leather in which leather to be chrome-retanned is contacted with basic chromium sulfate and a sulfite salt in an aqueous environment and thereafter the leather is contacted with an aldehyde to deposit chrome as Cr2O3 in the leather and form a leather having over 6 percent by weight of Cr2O3 based on the dry weight of the leather. Sodium sulfite or potassium sulfite can be used as the sulfite salt. Representative aldehydes which can be used are formaldehyde, glutaraldehyde, benzaldehyde, or a compound which in the presence of an acid is converted to an aldehyde.

Description

United States Patent [1 1 Dawson June 10, 1975 METHOD OF CHROME-RETANNING LEATHER [75] Inventor: William Orval Dawson, Milwaukee,

[52] U.S. Cl. 8/94.27; 8/94.21; 8-/94.26; 8/94.33 [51] Int. Cl. Cl4c 3/06 [58] Field of Search 8/94.21, 94.26, 94.27, 8/94.33

[56] References Cited UNITED STATES PATENTS 528,162 lO/l894 Heinzerling 8/94.27 2,997,363 8/1961 Pfirrmann 8/94.26 3,254,937 6/1966 Komarek et a1. 8/94.26 3,346,323 10/1967 Spahrkas et al. 8/94.26 3,482,925 12/1969 Schmid et al. 8/94.17 3,519,378 7/1970 Luck et al 8/94.26 3,551,089 l2/l970 Dawson et al. 8/94.27 3,558,262 l/l97l Duffy et al 8/94.27

OTHER PUBLICATIONS Wilson, The Chemistry of Leather Manufacture, 1929,

Vol. II ACS TS965W5, p. 611.

Gustavson The Chemistry of Tanning Processes 1956, pp. 339-40, TS967G8.

Primary ExaminerBenjamin R. Padgett Assistant ExaminerB. Hunt Attorney, Agent, or Firm-Merriam, Marshall, Shapiro & Klose [5 7 ABSTRACT An improved process of chrome-retanning leather in which leather to be chrome-retanned is contacted with basic chromium sulfate and a sulfite salt in an aqueous environment and thereafter the leather is contacted with an aldehyde to deposit chrome as Cr O in the leather and form a leather having over 6 percent by weight of Cr O based on the dry weight of the leather.

Sodium sulfite or potassium sulfite can be used as the sulfite salt. Representative aldehydes which can be used are formaldehyde, glutaraldehyde, benzaldehyde, or a compound which in the presence of an acid is converted to an aldehyde.

27 Claims, N0 Drawings METHOD OF CHROME-RETANNING LEATHER This invention relates to processes for producing leather from animal hides. More particularly, this invention is concerned with an improved process of producing leather by chrome-retanning.

Large quantities of animal hides are converted into leather. Although cattle hides are the most important raw material for tanners in producing leather, there is a considerable production of leather from calf, sheep, hog and goat hides.

The conversion of an animal hide into leather is done by tanning. Although tanning can be effected by using essentially vegetable materials, and particularly materials which contain appreciable amounts of tannin, such as the bark and wood of oak, chestnut and wattle, probably a considerably greater amount of leather is .produced by the processs of chrome-tanning.

Irrespective of the tanning process used, however, the animal hides are usually dehaired. One method of dehairing is to soak the hide in a lime solution containing additives designed to aid in hair removal and to then mechanically remove the hair. The dehaired hides, from which all flesh is removed by scraping, are then treated in a rotating drum with a deliming material such as ammonium chloride or ammonium sulfate to neutralize the lime. A pancreatic enzyme is added to the deliming solution to aid in bating and deliming and to further condition the hides. After being washed with water, the hides, after draining, are ready for the tanning process.

In the first step of a conventional chrome-tanning operation, the hides are pickled with a solution of an acid, usually sulfuric acid, and sodium chloride. A chrometanning solution prepared by reducing sodium bichromate in a conventional manner is then introduced into the drum. The drum is rotated during the tanning operation. The basicity of the chrome-tanning solution can vary consideraly. Normally, it will be in the range of about 25 to 50 percent. Furthermore, the conditions of chrome-tanning, such as the volume of the chrometanning liquor, the concentration of chromium salts and other ingredients in the liquor and the treatment time are all matters that are well known by those skilled in the art.

Following such a conventional chrome-tanning operation, the hides are sorted according to the use to which the leather ultimately will be put. Subsequently, at least in the United States, the chrome-tanned leather is split. In Europe, however, the leather generally is split after the hair is removed from the hide and before it is bated, pickled and chrome-tanned.

In conventional methods of leather production, the chrome-tanned leather in split form is then treated according to a wide variety of processes to obtain desirable characteristics such as softness, firmness, uniformity of temper, smoothness, grain break and color. Then the leather is fat-liquored, which is essentially the introduction of various water dispersible fats and oils into the leather to preserve and soften the leather.

Although the described general process for producing chrome-tanned leather is suitable for many types of leather production, it is often found that the resulting product lacks the desired softness, fullness and chrome content. Accordingly, to produce leather with these desirable properties and to raise the chrome content, it is common to subject the chrome-tanned leather to a chrome-retanning process.

In conventional chrome-retanning, the chromeretanning liquors used are generally similar to those used in the initial chrome-tanning process. Chromeretanning as presently practiced is a time-consuming operation and generally leaves considerable to be desired, both in the process and the resulting leather. Most of the time the operation leads to results far short of the desirable fullness, softness and increased chrome content sought in the leather. Furthermore, resistance to shrinkage in the presence of heat, and resistance to perspiration, generally are not improved substantially using conventional chrome-retanning processes. Very seldom can the chrome content of the leather on a dry basis be increased 2 to 4 percent of Cr O by a chromeretanning operation. Since the initial Cr O content of the chrome-tanned leather on a moisture free basis is in the neighborhood of about 2.5 to 3.5 percent, it is generally not possible by conventional chromeretanning operations to produce leather having much over 5.5 percent Cr O on a moisture free basis.

Dawson et al. US. Pat. No. 3,551,089 discloses a chrome-retanning method using ammonium zirconyl carbonate. This procedure raises the chrome content of a chrome-retanned leather from a high of about 3.5 percent to over 4.5 percent and up to nearly 6 percent. However, higher amounts than 6 percent of chrome in the leather are desired so as to improve the heat stability of the leather and to generally improve its properties.

It has been found according to the present invention that improved chrome-retanned leathers can be produced by subjecting an animal hide, previously initially chrome-tanned by conventional procedures, to the action of a basic chrome-retanning solution and a sulfite salt followed by the addition of an aldehyde to the solution while in contact with the leather. The process results in deposition of chrome calculated as Cr O in the leather in amounts from 50 to 200 percent higher than is achieved by conventional chrome-retanning procedures.

Treatment of a chrome-tanned leather with a basic chrome-retanning solution followed by treatment with an aldehyde does not effect chrome-retanning of the leather because the chrome is not precipitated from solution unless the pH is raised and if not precipitated it does not combine with the leather and hence it will be readily removed during washing or other chemical applications. However, if the pH is raised by adding a base, such as sodium hydroxide, to the solution, the Cr O is precipitated on the leather and in the solution, rather than in the leather.

A basic chrome-retanning solution containing a sulfite salt is not suitable for effecting chrome-retanning without an aldehyde because the sulfite salt raises the pH and the basicity of the chromium sulfate solution, solubilizes the chrome and masks the solution so that precipitation of chrome does not occur, even at the higher pH. The same result occurs when a chrometanned leather is treated with a basic chrome-retanning solution followed by treatment of the leather with a solution of a sulfite salt. However, if such a leather treatment is followed by treatment of the leather with an aldehyde while the chrome and sulfite are in contact with the leather, the masking or complexing effect exerted by the sulfite on the chrome in solution is overcome by the aldehyde. The aldehyde causes the pH to rise quite quickly and the chrome to precipitate and deposit in the leather, with full exhaustion of the chrome from solution.

The process of the invention can be practiced using any conventional chrome-retanning solution containing basic chromium sulfate. The basicity of such solutions can vary widely but usually will be about 25 to 60 percent. A chrome-retanning solution can be used having a volume and containing an equivalent ofCr O sufficient to supply enough chrome so that the chrome increase, calculated as Cr O in the leather will be to the extent desired but, of course, within the limits of the invention. Normally, the chrome-retanning solution used should contain sufficient Cr O to provide about 1 to 6 percent by weight of Cr O based on the dry weight of the leather of additional Cr O above the amount deposited in the leather by conventional, initial chrometanning. The chrome solution will generally have a pH of about 4.5 to 3.7 or lower.

Any suitable sulfite salt which is soluble under the conditions used in the process can be employed. The alkali metal sulfite salts are presently considered most suitable. Sodium sulfite and potassium sulfite are par ticularly suitable since they are readily available. While calcium sulfite and other alkaline earth metal sulfite salts such as magnesium sulfite can be used, as well as ammonium sulfite, these salts are not considered as suitable as the alkali metal salts.

Although the amount by weight of Cr O in the chrome-retanning solution with respect to the amount by weight of sulfite salt used in the process is not narrowly critical, it is generally advisable to employ these materials in a ratio of about 1 to 4 parts by weight of sulfite salt per one part by weight of Cr O equivalent in the solution. On a molecular weight basis, the equivalent of about one mole of Cr O should be present for each 2 to 4 moles of sulfite salt.

It presently appears that any aldehyde can be used in practicing the chrome-retanning process of this invention. Thus, straight and branched chain hydrocarbon monoaldehydes such as formaldehyde, acetaldehyde and caproaldehyde; aryl aldehydes such as benzaldehyde and l-naphthaldehyde; polyaldehydes such as glyoxal, malonaldehyde, glutaraldehyde and phthalaldehyde; dialdehyde starch; and compounds which convert to aldehydes readily, can be used in the process. A series of commercial compounds marketed under the trade name Oxazolidine are particularly useful in the process even though they are not aldehydes because in the presence of an acid they are converted to aldehydes. Specific Oxazolidines which can be used in this way are Oxazolidine T of the formula cn on O N O and having the chemical name of 5-hydroxymethyl-laza-3,7-dioxabicyclo[3,3,0]octane;

Oxazolidine E of the formula and having the chemical name of 5-ethyl-l-aza-3,7- dioxabicyclo [3,3,0]octane; and

Oxazolidine A of the formula HN O and having the chemical name of 4,4-dimethyl-l ,3- oxazoline. These compounds, and others of similar structure, in the presence of an acid such as sulfuric acid, hydrochloric acid, phosphoric acid and acetic acid, or an acid salt such as sodium acid sulfate or monosodium dihydrophosphate, converts to an aldehyde by ring cleavage. The resulting aldehyde functions suitably in the chrome-retanning process of this invention.

The amount of aldehyde used in the process is not especially critical. However, enough aldehyde is to be used to react with all of the sulfite salt to form a basic byproduct of the reaction according to the reaction:

wherein R is hydrogen or an organic residue and M is a metallic ion. The aldehyde combines with the sulfite by omega sulfonation to release a base, such as sodium hydroxide when M is Na. The basic by-product MOH, and advisably sodium hydroxide, raises the pH of the chrome-retanning solution and thereby causes the chrome to deposit in the leather. It is generally advisable to use about 0.1 to 2 parts by weight of an aldehyde per each part by weight of sulfite salt used in the treatment. It should be understood however that the best ratio or proportion to use is to be determined for the specific materials employed using the normal skill in the art. It is to be expected that the ratios may vary from one aldehyde to another according to the reactivity of the aldehyde and whether it is a monoaldehyde or polyaldehyde.

The ratio of equivalents of Cr O used in the process to the amount of aldehyde can vary quite widely but usually will be in the ratio of 1 part by weight of Cr O to 0.25 to 3 parts by weight of an aldehyde on a percent aldehyde basis.

It should be understood with respect to all of the ra tios presented herein that the use of specific materials may require the use of amounts outside of the stated typical ratios. Nevertheless, the use of such ratios and materials is to be included within the scope of the invention.

It is advisable in practicing the invention to first bring the chrome-tanned leather which is to be chromeretanned into contact with a basic solution of chromium sulfate. The leather, for example, can be placed in a conventional tanning drum and a basic chromeretanning solution, devoid of a sulfite salt and an aldehyde, can be added followed by the addition of the sulfite salt and then by the addition of the aldehyde. After the separate addition of each material in the described order the drum can be rotated to bring the materials into intimate contact with all areas of the leather.

Although it is advisable to first treat the chrometanned leather with a basic chrome-retanning solution containing no sulfite salt and no aldehyde, it is feasible to treat the leather with a basic chrome-retanning solution containing a sulfite salt but no aldehyde. The sulfite salt can be added to a basic chrome-retanning solution and the solution then added to a leather processing drum containing the leather to be chromeretanned. Although the sulfite salt slowly causes the pH of the solution to increase, i.e., become more basic, the chrome does not precipitate out of the solution until after the aldehyde is added. The addition of the aldehyde results in precipitation of the chrome into the leather, with essentially complete exhaustion of the chrome from the solution and production of the desired chromeretanned leather.

The chrome-retanning process can be effected at any temperature found suitable for the conditions and equipment although generally the solutions should be employed at a temperature of about 70 to 130F. The time of treatment after all the ingredients used in the process have been brought in contact with the leather is not considered narrowly critical. The treatment can be continued for such time as is necessary to effect deposit of the chrome in the leather. Under normal conditions this will take from about minutes to 1 hour to completely exhaust the chrome from the solution. It should be understood that the total amount of chrome in solution should not be larger than the amount of chrome which the leather can take up since the rest would be wasted. When the process is practiced properly all the chrome used will be exhausted from solution and be taken up by the leather.

Leathers that are chrome-retanned according to the invention have chrome contents based on Cr O of more than 4 percent by weight of dry leather and generally will contain 8 to 9 percent or more of Cr O depending upon the amount desired in the leather. Such large amounts of chrome are deposited in the leather without deleterious effects on the leather and, to the contrary, with the production of leathers having superior properties.

After the chrome-retanning is completed, the leather can be further processed using conventional procedures of coloring and fat-liquoring. The leather so produced has excellent properties, is more heat stable than other leathers because of its high chrome content, has good fullness, is soft and is tight breaking.

EXAMPLE 1 Eight hundred pounds of chrome-tanned split and shaved cow hides (8O sides) containing 3 percent by weight of chrome calculated as Cr O on the dry weight of the leather was placed in a rotating drum and floated with 192 gals. (U.S.) of water at 115F. The water equalled 200 percent by weight based on the weight of split and shaved leather containing about 50 percent by weight of water. The leather was washed over a 20 minute period using 840 gals. (U.S.) of water at 115F.

The drum was drained of water and then the leather was floated in 72 gals. (U.S.) of water at 115F. To the leather was then added 19.2 gals. (U.S.) ofa 42 percent basic chrome liquor at 115F. calculated to provide 3 percent by weight of chrome as Cr- O to the leather on a wet leather basis. The leather was drummed for 15 minutes and then pounds of anhydrous sodium sulfite was added followed by 45 minutes of drumming. The solution had a pH of 5.75.

Eighty pounds ofa 16 percent by weight sulfuric acid solution in 14.4 gals. (U.S.) of water was added to 80 pounds of a 50 percent aqueous solution of 5-ethyl-1- aza-3,7-dioxabicyclo [3,3,0]octane sold as Oxazolidine E. The resulting mixture was added to the leather in the drum, The leather was drummed for 45 minutes. Complete exhaustion of chrome into the leather from the solution was achieved. On a dry leather basis the leather therefore theoretically contained at least 9 per cent by weight of chrome calculated as Cr O The pH of the solution in the drum was 5.9.

Although the chrome-retanning according to the invention is complete at this point, additional treatments of the leather are performed according to conventional procedures to obtain a commercial, finished leather. The following procedure is representative of those which can be used to further process the chromeretanned leather.

The chrome-retanned leather was washed in the drum for 20 minutes using 840 gals. (U.S.) of water at F. The water was drained from the drum. The leather was then floated in the drum in 72 gals. (U.S.) of water at 120F,

To the drummed leather was added 40 pounds of an anionic aminoplast resin (Chemtan R-9) in 28.6 gals. (U.S.) of water at 120F. The leather was drummed 10 minutes and then 16 pounds of dry boric acid was added. The leather was then drummed for 20 minutes.

The leather was then dyed using 3 pounds of yellow dye (Ortolan Yellow RR), 1 pound of beige dye (Lurazol Beige), and 1 pound of brown dye (Luganil Brown N36). The dyes were added to 24 gals. (U.S.) of water, the solution was boiled, cooled to 120F. and then added to the drummed leather. The leather was drummed for 20 minutes.

To the leather was added 48 pounds of blended vegetable tannins and 6.4 gals. (U.S.) of a 42 percent basic chrome solution calculated to add 1 percent by weight of chrome as Cr O to the leather in 28.6 gals. (U.S.) of water at 120F. The leather was drummed for 30 minutes. The pH of the solution was 4.2.

Two pounds of formic acid in 9.6 gals (U.S.) of water at 80F. was added to the leather to set the dye. The leather was washed 20 minutes with water at F. The leather was drained of water and then floated in 96 gals. (U.S.) of water at 130F. To the leather was then added 44 pounds of a sulfated mixture of vegetable, fish and animal oils in 24 gals. (U.S.) of water at 130F. The leather was then drummed for 45 minutes.

To the leather was added 20 pounds of a cationic emulsified raw oil in 19.4 gals. (U.S.) of water at 130F. as a topping oil. The leather was drummed 15 minutes. The solution pH was 4.2. The leather was then removed from the drum, horse smoothed and dried.

A st'ratographic analysis was made for chrome calculated as Cr O in the leather. The results of this process are given in Table 1 together with comparative data for a conventional chrome-retanned leather and for a regular nonchrome-retanned leather.

Table 1 Percent C r on a dry basis Example 1 Conventional Regular chromechromenonchromeretanned retanned retanned Grain slice 1 1.7 5.4 2.9 Second slice 10.8 5.8 3.5 Third slice 8.1 5.8 3.4 Fourth slice 9.4 5.8 3.2 Flesh slice 10.7 5.4 2.6

EXAMPLE 2 A IOO-pound group of nine chrome-tanned split sides shaved to 4.25 to 4.75 oz. (1 oz. equals 0.4 mm. of leather thickness) containing 3 percent Cr O based on the leather, dry weight, were placed in a drum and washed 10 minutes at 115F. with water and drained. The leather was floated in 7.5 gals. (U.S.) (50 percent by weight) of water at 1 15F. and then 3 percent Cr O based on the leather, wet weight, as a 42 percent basic chrome liquor was added at 1 15F. and rotated for 15 minutes. The pH of the solution in the drum was 3.4. Then to the leather was added 10 percent by weight based on the wet weight of the leather, of anhydrous sodium sulfite following which the drum was rotated for 60 minutes.

An amount of sulfuric acid equal to 1.6 percent by weight of the wet leather was diluted with an amount of water equal to 10 percent by weight of the wet leather at 80F. The resulting solution was added to an amount of a 50 percent solution of 5-ethyl-l-aza-3,7- dioxabicyclo[3,3,0]octane, sold under the trade name Oxazolidine E, in water equal to percent of the weight of the wet leather. The drum was then rotated for 45 minutes. The pH of the solution in the drum went from 5.2 to about 6.0 to 6.5. The chrome was completely exhausted.

The leather was then washed 5 minutes at 120F., drained and floated in 50 percent by weight of water at 120F. The leather was then finished according to conventional procedures. It contained 9 percent by weight of Cr O on a dry leather basis.

EXAMPLE 3 The procedure of Example 2 is followed using an equal amount of glutaraldehyde in place of Oxazolidine E and without use of the sulfuric acid. The leather obtained has a high chrome content which may average 9 percent by weight as Cr O EXAMPLE 4 The procedure of Example 1 is followed using an equal amount of formaldehyde in place of Oxazolidine E and without use of the sulfuric acid. The leather obtained has a chrome content of at least 9 percent by weight as Cr O The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifcations will be obvious to those skilled in the art.

What is claimed is:

1. In the process of chromeretanning leather, the improvement which comprises contacting a leather to be chrome-retanned with basic chromium sulfate and a sulfite salt in an aqueous environment and thereafter contacting the leather with an aldehyde to deposit chrome as Cr O in the leather and form a leather having over 6 percent by weight of Cr O based on the dry weight of the leather.

2. The process of claim 1 in which the basicity of the chromium sulfate in contact with the leather is about 25 to 60 percent.

3. The process of claim 2 in which the solution is at a temperature of about to F during contact with the leather. 7

4. The process of claim 1 in which the sulfite salt is an alkali metal salt.

5. The process of claim 4 in which the alkali metal salt is sodium sulfite or potassium sulfite. I

6. The process of claim 1 in which the aldehyde is formaldehyde. 7

7. The process of claim 1 in which the aldehyde is glyoxal.

8. The process of claim 1 in which the aldehyde is glutaraldehyde.

9. The process of claim 1 in which the aldehyde is benzaldehyde.

10. The process of claim 1 in which the aldehyde is acetaldehyde.

11. The process of claim 1 in which the aldehyde is formed by acidifying a member of the group consisting of S-hydroxymethyL l -aza-3 ,7-dioxabicyclo[3 ,3 ,0]octane, S-ethyl- 1 -aza-3 ,7-dioxabicyclo[3 ,3,0 ]octane and 4,4-dimethyl-l ,3-oxazolidine.

12. In the process of chrome-retanning leather, the improvement which comprises:

contacting a leather to be chrome-retanned with an aqueous solution of basic chromium sulfate; thereafter contacting the leather with a sulfite salt in aqueous solution; and

thereafter contacting the leather with an aldehyde in aqueous solution, thereby depositing chrome as Cr O in the leather to form a leather having over 6 percent by weight of Cr O based on the dry weight of the leather.

13. The process of claim 12 in which the basicity of the solution is about 25 to 60 percent.

14. The process of claim 12 in which the solution is at a temperature of about 70 to 130F during contact with the leather.

15. The process of claim 12 in which the sulfitesalt is an alkali metal salt. I

16. The process of claim 15 in which the alkali metal salt is sodium sulfite or potassium sulfite.

17. A chrome-retanning solution according to claim 12 in which the sulfite salt is sodium sulfite or potassium sulfite, and the aldehyde is a member of the group consisting of formaldehyde, glyoxal, glutaraldehyde, acetaldehyde, dialdehyde starch, benzaldehyde and an aldehyde formed by acidification of a member of the group consisting of S-hydroxymethyl-l-aza-3,7-dioxabicyclo[ 3 ,3,0]octane, 5-ethyl-1-aza-3,7-dioxabicyclo[ 3,3,0]octane and 4,4-dimethyl-l ,3-oxazolidine.

18. The process of claim 12 in which the amount of Cr O in the leather is increased about 1 to 6 percent by weight, by the chrome-retanning process, over the Cr O content of the leather before said chromeretanning.

19. In the process of chrome-retanning leather, the improvement which comprises:'

contacting a leather to be chrome-retanned with an aqueous solution of basic chromium sulfate with said solution containing a sulfite salt; and

thereafter contacting the leather with an aldehyde in aqueous solution,

thereby depositing chrome as Cr O in the leather to form a leather having over 6 percent by weight of Cr O based on the dry weight of the leather.

20. The process of claim 19 in which the basicity of the solution is about 25 to 60 percent.

21. The process of claim 19 in which the solution is at a temperature of about 70 to 130F during contact with the leather.

22. The process of claim 19 in which the sulfite salt is an alkali metal salt.

23. The process of claim 22 in which the alkali metal salt is sodium sulfite or potassium sulfite.

24. A chrome-retanning solution according to claim 19 in which the sulfite salt is sodium sulfite or potassium sulfite, and the aldehyde is a member of the group consisting of formaldehyde, glyoxal, glutaraldehyde, acetaldehyde, dialdehyde starch, benzaldehyde and an aldehyde formed by acidification of a member of the group consisting of 5-hydroxymethyl-l-aza-3,7-dioxabicyclo[ 3 .3 ,Oloctane, S-ethyll -aza-3 ,7-dioxabicyclo[ 3,3,01octane and 4,4-dimethyl-l ,3-oxazolidine.

25. The process of claim 19 in which the amount of Cr O in the leather is increased about 1 to 6 percent by weight, by the chrome-retanning process, over the Cr O content of the leather before said chromeretanning.

26. A chrome-retanning aqueous solution comprising a sulfite salt, an aldehyde and basic chromium sulfate.

27. A chrome-retanning solution according to claim 26 in which the sulfite salt is sodium sulfite or potassium sulfite, the aldehyde is a member of the group consisting of formaldehyde, glutaraldehyde, acetaldehyde, glyoxal, dialdehyde starch, benzaldehyde or an aldehyde formed by acidification of S-hydroxymethyll-aza-3 ,7-dioxabicyclo[ 3 ,3 ,0]octane, S-ethyll -aza- 3,7-dioxabicyclo[3,3,0]octane or 4,4-dimethyl-l,3-

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 1 3,888,625

DATED 3 June 10, 1975 INVENT0R(5) I William Orval Dawson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 8, line 59, "solution" should be process; column 9, line 25, "solution" should be -process.

Signed and Scaled this fifteenth D3) of June 1976 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner vjlarems and Trademarks

Claims

1. IN THE PROCESS FOR CHROME-RETANNING LEATHER, THE IMPROVEMENT WHICH COMPRISES CONTACTING A LEATHER TO BE CHROMERETANNED WITH BASIC CHROMIUM SULFATE AND A SULFITE SALT IN AN AQUEOUS ENVIRONMENT AND THEREAFTER CONTACTING THE LEATHER WITH AN ALDEHYDE TO DEPOSIT CHROME AS CR2O3 IN THE LEATHER AND FORM A LEATHER HAVING OVER 6 PERCENT BY WEIGHT OF CR2CO3 BASED ON THE DRY WEIGHT OF THE LEATHER.

3. The process of claim 2 in which the solution is at a temperature of about 70* to 130*F during contact with the leather.

4. The process of claim 1 in which the sulfite salt is an alkali metal salt.

5. The process of claim 4 in which the alkali metal salt is sodium sulfite or potassium sulfite.

6. The process of claim 1 in which the aldehyde is formaldehyde.

7. The process of claim 1 in which the aldehyde is glyoxal.

8. The process of claim 1 in which the aldehyde is glutaraldehyde.

9. The process of claim 1 in which the aldehyde is benzaldehyde.

10. The process of claim 1 in which the aldehyde is acetaldehyde.

11. The process of claim 1 in which the aldehyde is formed by acidifying a member of the group consisting of 5-hydroxymethyl-1-aza-3,7-dioxabicyclo(3,3,0)octane, 5-ethyl-1-aza-3,7-dioxabicyclo(3,3,0)octane and 4,4-dimethyl-1,3-oxazolidine.

12. In the process of chrome-retanning leather, the improvement which comprises: contacting a leather to be chrome-retanned with an aqueous solution of basic chromium sulfate; thereafter contacting the leather with a sulfite salt in aqueous solution; and thereafter contacting the leather with an aldehyde in aqueous solution, thereby depositing chrome as Cr2O3 in the leather to form a leather having over 6 percent by weight of Cr2O3 based on the dry weight of the leather.

14. The process of claim 12 in which the solution is at a temperature of about 70* to 130*F during contact with the leather.

15. The process of claim 12 in which the sulfite salt is an alkali metal salt.

17. A chrome-retanning solution according to claim 12 in which tHe sulfite salt is sodium sulfite or potassium sulfite, and the aldehyde is a member of the group consisting of formaldehyde, glyoxal, glutaraldehyde, acetaldehyde, dialdehyde starch, benzaldehyde and an aldehyde formed by acidification of a member of the group consisting of 5-hydroxymethyl-1-aza-3,7-dioxabicyclo(3,3,0)octane, 5-ethyl-1-aza-3,7-dioxabicyclo(3,3, 0)octane and 4,4-dimethyl-1,3-oxazolidine.

18. The process of claim 12 in which the amount of Cr2O3 in the leather is increased about 1 to 6 percent by weight, by the chrome-retanning process, over the Cr2O3 content of the leather before said chrome-retanning.

19. In the process of chrome-retanning leather, the improvement which comprises: contacting a leather to be chrome-retanned with an aqueous solution of basic chromium sulfate with said solution containing a sulfite salt; and thereafter contacting the leather with an aldehyde in aqueous solution, thereby depositing chrome as Cr2O3 in the leather to form a leather having over 6 percent by weight of Cr2O3 based on the dry weight of the leather.

21. The process of claim 19 in which the solution is at a temperature of about 70* to 130*F during contact with the leather.

22. The process of claim 19 in which the sulfite salt is an alkali metal salt.

24. A chrome-retanning solution according to claim 19 in which the sulfite salt is sodium sulfite or potassium sulfite, and the aldehyde is a member of the group consisting of formaldehyde, glyoxal, glutaraldehyde, acetaldehyde, dialdehyde starch, benzaldehyde and an aldehyde formed by acidification of a member of the group consisting of 5-hydroxymethyl-1-aza-3,7-dioxabicyclo(3,3,0)octane, 5-ethyl-1-aza-3,7-dioxabicyclo(3,3, 0)octane and 4,4-dimethyl-1,3-oxazolidine.

25. The process of claim 19 in which the amount of Cr2O3 in the leather is increased about 1 to 6 percent by weight, by the chrome-retanning process, over the Cr2O3 content of the leather before said chrome-retanning.

27. A chrome-retanning solution according to claim 26 in which the sulfite salt is sodium sulfite or potassium sulfite, the aldehyde is a member of the group consisting of formaldehyde, glutaraldehyde, acetaldehyde, glyoxal, dialdehyde starch, benzaldehyde or an aldehyde formed by acidification of 5-hydroxymethyl-1-aza-3,7-dioxabicyclo(3,3,0)octane, 5-ethyl-1-aza-3,7-dioxabicyclo(3,3,0)octane or 4,4-dimethyl-1,3-oxazolidine.